The present invention relates generally to document processing operations and, more particularly, to a system and method for parameter based visual characteristic control.
For example, in a typical laser printer, rollers pull a sheet of paper from a tray and through a “charge roller,” which gives the paper an electrostatic charge. At the same time, a printing drum is given an opposite charge. The surface of the drum is then scanned by a laser, discharging portions of the drum surface, leaving only those points corresponding to the desired text and image with a charge. This charge is then used to adhere toner to the drum surface. The paper and the drum are then brought into contact, the differing charges causing the toner to adhere to the paper. The paper then travels between “fusing rollers” which heat the paper and melt the toner, fusing the toner to the paper.
Corresponding process occur in direct deposition printers, such as dot matrix printers, inkjet printers, and the like.
A printer suitably adjusts image contrast by applying a “contrast curve” to image data prior to printing therefrom. A shape of the contrast curve is determined by a “contrast setting,” typically a number ranging from −100 to +100. By way of example, a setting of 0 results in no change in the image, while settings less than zero reduce contrast and settings greater than zero increase contrast.
Increasing contrast increases the differences between light and dark portions of an image so that light areas become lighter and dark areas become darker. Decreasing contrast reduces these differences. By manipulating contrast in this way, users can improve the quality of the images.
Contrast curves are typically implemented through a look up table (LUT) that relates input and output pixel values between input image data and adjusted, output image data. Input and output pixel values are often normalized in the LUT such that their values range between 0 and 1. When so normalized, 0 suitably represents pure black and 1 suitably represents pure white.
In keeping with the above example, the LUT is used to change the magnitude of the charge, thereby increasing or decreasing contrast. As also described above, the input values relate to the image, while the output values are the application of the curve to the image that is, in turn, printed by the printer. Thus, by changing the characteristics of the LUT and use thereof, a user selects a desired contrast.
However, use of such a large population of individual LUTs for contrast adjustment is not without drawbacks. For example, the use of a LUT that contains values for numerous contrast levels involves the storage of considerable amounts of data, and the storage and processing of such large amounts of data becomes burdensome. Further, such a population of pre-defined LUTs is inflexible. In a similar manner, by manipulating the transfer characteristics, the entire image can be made lighter or darker.
Thus, there exists a need for a system and method that uses a simple arithmetic function for setting parameters that can lighten, darken, enhance or reduce contrast.